In recent years, the touch panel is more and more popular, and may replace the mouse and the keyboard in the future. Touch panels have been widely used in home appliances, communication devices, and electronic information products such as a personal digital assistant (PDA), and a game input interface. Now, a touch panel is always integrated with a display panel, so a user can touch a position on the touch panel corresponding to a displayed image of the display panel to select an operation directly. Therefore, such a combined structure of the touch panel and the display panel provides users with better portability and more comfortable input operation.
There are many types of touch panels, such as resistance touch panel, capacitive touch panel, infrared sensing touch panel, electromagnetic sensing touch panel, and acoustic wave sensing touch panel, according to different technology principles. Herein, the capacitive touch panel is a comparatively good type because of its high sensitivity, low cost, and simple structure. Theoretically, the capacitive touch panel detects the capacitance changes of the electrodes generated by a human body or other grounded material to determine the touch position.
Referring to FIG. 1, the conventional capacitive touch panel includes a circuit pattern, made of conductive materials, formed on a substrate. The circuit pattern has x-axis (X0-X7) and Y-axis (Y0-Y4) electrode strips. In operation, a control circuit scans the electrode strips sequentially. When a finger or other grounded conductors touch a position (shown as black area) of the capacitive touch panel, the capacitance of the X-axis electrode strips and Y-axis electrode strips which be touched change, and after sensing the capacitance of the electrode strips, the control circuit will determine the X-axis and Y-axis coordinates of the touched position based on the capacitance changes. In some applications, a plurality of diamond shaped conductive cells arranged along the X-axis and Y-axis directions are used to replace the conductive strips shown in FIG. 1.
FIG. 2 shows the structure of the conventional capacitive touch panel with single sided routing. A plurality of conductive traces 102 connects one ends of the X-axis (X0-X6) and Y-axis (Y0-Y4) conductive cells 104 of the conductive touch panel to a controller 106 for transferring electrical signals to the controller 106 to analyze.
One aspect of electronic performance of a touch panel is that the total impedance of the conductive strips and conductive traces should be considered. Generally a high impedance will lead to a rapid attenuation of electrical signals, thus the sensitivity of the touch panel will be reduced. When a plurality of diamond shaped conductive cells replace the conductive strips, the connection between the adjacent transparent conductive cells will have high impedance.
Further referring to FIG. 3, a single row of diamond shaped conductive cells shown in FIG. 2 is illustrated with indicated symbols C, B, A. The single row is connected to the controller (not shown) via the end C. In operation, the electrical signals are transmitted from the end C to the midpoint B, and then to the other end A. Along the direction of the transmission of the electrical signals (C-B-A), the impedance of the single axis gradually increases and the signal to noise ratio will get smaller, especially at higher frequencies. In that case, for the same touched area, the signal to noise ratio at the point close to end C is bigger than the signal to noise ratio at the point close to end A. Furthermore, if the impedance increases to a certain level, signal to noise ratio may be low such that it is no longer possible to process the signal. Usually, scanning frequency can be reduced to keep the signal to noise ratio similar at the end C and end A of the row. However, if the scanning frequency is reduced, other problems will occur, such as low scanning speed and low detecting sensitivity.
Therefore, a new touch panel having not only a comparatively high scanning speed but also a comparatively low impedance is needed to overcome said problems.